The present invention relates to a hot continuous-rolling system. More particularly this invention concerns a roll stand with vertical rolls for such a system.
It is known to produce rod or wire in a continuous-casting system where molten metal is formed either into a flat strip that is cut longitudinally (see Japanese 60-130401) into a plurality of strands that are then handled jointly in a parallel system, or the strands are directly formed from molten metal and also then handled jointly in a parallel system. Regardless of how the strands are continuously produced from molten metal, they are passed through succeeding vertical- and horizontal-roll stands that reduce the cross-sectional size of each of the strands, with of course simultaneous increase in length, while improving the grain structure and imparting to them the desired cross-sectional shape.
Such rolling of wire and rod is extremely difficult and technical. Output speeds of 30 m/sec to 100 m/sec for straight rod are employed, making the equipment very difficult to control and operate in a continuous process. Beyond a certain speed, production problems become so great that the extra productivity is not really attainable.
In a known system a continuously cast generally square-section billet measuring 160 mm on a side is produced at a rate of 37 ton/h so that it must be rolled at 3 m/min, or 0.05 m/sec. In order to produce from this starting workpiece round-section wire of 8.5 m diameter it is necessary to use 18 rolling stands. The speed into the first roll stand must be three times the casting speed.
In such systems where the finished product is wound up, the EDEMBOR system, and in German 4,009,861 of Hoffmann, it is possible to produce a finished product smaller than 5.5 mm in diameter by using several rolling lines. To do this, however, extremely high speeds are used. Starting with a standard 150 mmxc3x97150 mm billet with a starting speed of 0.1 m/sec, it is necessary to accelerate to 300 m/sec by the time it is reduced to a rod 3 mm in diameter. Such speeds are almost impossible to use without jamming. Furthermore the rolling stands must be arranged in two or three lines to achieve the desired finished product, making the overall rolling system very large and requiring technically difficult direction changes.
Japanese 57-193205 process a wide flat strip that is cut into a plurality of parallel rectangular-section strands. They are rolled out, then put through another rolling line before they become the finished product. Thus this process is discontinuous and somewhat slow, having such low productivity as to not represent a significant advantage over the other above-described systems.
U.S. Pat. No. 6,035,682 of Dorigo describes another system where a flat strip is slit longitudinally and rolled into oval-section rods by horizontal rolls that have staggered rolling surfaces that serve to vertically offset adjacent rods from each other as they are being rolled. This system starts with a strip less than 80 mm, preferably 50 mm, in thickness. It must be reheated before rolling. During the rolling the strands must be rotated through 90xc2x0 so that all edges can be rolled by the succeeding horizontal-roll mills, substantially complicating the operation of the machine. The strip must be rolled out before it is longitudinally slit, producing a longitudinal grain structure that, once slit, impair the strength of the finished workpiece.
It is therefore an object of the present invention to provide an improved rolling system.
Another object is the provision of such an improved rolling system which overcomes the above-given disadvantages, that is which is capable of producing a finished product at most 5.5 mm in diameter without difficulty.
A further object is to provide an extremely compact rolling system.
A rolling system has according to the invention a plant producing a plurality of continuously advancing and parallel hot metal strands, a vertical-roll stand receiving the strands, and a horizontal-roll stand. The vertical-roll stand has an upstream row of vertical pairs of rolls and, immediately downstream therefrom in a movement direction of the strands, a downstream row of vertical pairs or rolls. The rows extend parallel to each other and transversely to the strands with each roll pair defining a nip and the nips of the downstream roll pairs staggered transverse to the direction between the nips of the upstream roll pairs. Every other the strand passes by the upstream roll pairs and through the nips of the downstream roll pairs and the remaining strands pass through the nips of the upstream roll pairs and by the downstream roll pairs. The horizontal-roll stand is aligned in the direction with the vertical-roll stand and has a pair of horizontal rolls forming a plurality of nips aligned in the direction with the nips of the vertical-roll stand. The rolls are rotated to draw the strands downstream through the nips.
This rolling system is extremely compact. It subjects the strands to rolling in two orthogonal directions so as to produce a uniform cross-sectional shape and ideal flow of the metal so that the resultant rod is very strong and smooth. Not only is the system very short in the travel direction, but as a result of the staggering of the vertical rolls it is relatively narrow perpendicular to this direction, guiding the strands in a fairly straight line from the location where they are created by casting to the downstream end where the finished product is cut to length or wound on coils.
According to the invention the strands are cast continuously of molten metal. This can be done with a die having a slot-shaped hole configured to produce a flat strip having a plurality of ridges interconnected by thin integral webs. The flat strip is then slit longitudinally at the webs into the strands. Alternately the die has a plurality of separate passages arranged in a line and each producing a respective one of the strands. In the latter case the die passages are curved.
In accordance with the invention the die has at least one throughgoing passage and is formed along the passage with an upstream compartment and a downstream compartment. Coolants at different temperatures are circulated through the compartments so as to control the strand production accurately.